Visual indicator for radio direction finders and measuring systems



June 27, 1933. J. D. R. FREED 1,915,780

VISUAL INDICATOR FOR RADIO DIRECTION FINDERS AND MEASURING SYSTEMS FiledApril 25, 1929 $51 m S ate m Patented June 27, 1933 Nr 1. tries fJosnrn. Din. renal), on new YORK, N. Y.-

visual. INDICATOR" non RADIO DIRECTION nrnnnns enn MEASURING SYSTEMSApplication filed April 25,

My invention relates to radio direction finder and measuring systems andparticularly has for its object a novel method for visually determiningthe direction of the received signal.

Another object of my invention is-its application to the navigationofaircraft, boats, and the location of hidden mineraland oil deposits. f

19 In the past it has been customary toemploy in such systems an oralindicator or telephone receiver; some inventions have substituted a neonlamp which at best is very crude and unreliable becausethe accuracyattained with such devices varies with the sensitiveness of theparticular operators hearing ability and in the case of the neon lampmany errors occur into any reading becausesuch methods are qualitativerather than quantitative indications. v p

I overcome the above deficiencies the employment of an improved. typeofquantitative indicator whereby the pilot, navigating officer oroperator can more accuratelydetermine his direction or position by theminimum position of the loop antenna. The invention will be more clearlyunderstood from the following description when the same is read withreference to the accompanying drawing.

The figure of the drawing illustrates diagrammatically a tuned radiofrequency thermionic receiver of the neutrodyne type, in which 2, 3, 4and 5 represent four stages of 5 radio frequency amplification, eachofsaid radio frequency stages of amplification is electromagneticallyand electrostatically shielded from one another. 6 is a thermionicdetector, the output circuit of which is connected with the inputcircuit of an audio frequency amplifier 7 and 8. 9 is'another rectifiercomprising a thermionic tube 10, having a plate element 11, a gridelement 12 and a filament 13 with a milliammeter 14 connected 4 incircuit so that one side is in circuit with the grid and plate of thethermionic tube 10 on the other side connected to the secondary windingof the audio frequency transformer of the last audio frequencyamplifying stage 5 8. Y

. obviously impossibleto dofthi's if the ob- 1929. semi n6. 357,931.

Current supply and the various voltages for operation of the'wholesystem are indicated in'the drawing and therefore it is felt no detailedexplanation is necessary.

Maximum signal intensity is obtained when the plane of the loop antenna1 lies in the direction ofthe source of'transmission, for example aradio beacon. If the source of transmission is at right angles to theplane of the rotatable loop antenna 1, then the signal intensity iszero. In all other directions the intensity of the signal varies fromzero to maximum and will be so indicated quantitatively byithe pointer15 of the milliammeter 13. l f I i It is therefore apparentthat'if therotatable loop antenna is of sufiiciently small dimensions to permitrotation about its Vertical axis, signals transmitted from any givensource'will be received with raying angles of intensity until therotatable loop antenna becomes normal. or at right angles to thedirection in which the transmitting source lies, at which time thesignal intensity becomes zero. This position of silence or minimumreading observed on my quantitative indicator is critical, andis used toindicate with a great degree of accuracy the line of direction of thetransmitting source. 7

Now when the pilot of an airplane, navigating officer of a ship or anoperator exploring for hidden mineralor oil deposits, desires to knowthe direction in which his plane or ship is traveling, in other words,his exact position, he will rotate the loop antenna 1 until he picks upthe desired signal and while so locating or changing the position of thesaid loop antenna he is careful to observe the position of the needle orpointer 15 of the milliammeter 14, thereby accurately determining theminimum position of the loop antenna, in that the loop antenna might beset at a position which gives a small but determinable value of currentand then pass through the minimum position to the position where thesame amount of current is again obtained. If the part covered in thisoperationis divided by two, it will correspond with the minimum positionof the loop antenna. It is r receiving and amplifying system may beemployed in connection withhis invention and that the'drawing isintended to be illustrative and not limitative.

"Having thus described my invention and illustrated its use, what Iherein claim as new and desire to secure by Letters Patent, is thetollowin-g In a radio direction finder system; a loop; means forgrounding themi dpoint of said loop, said r loop being symmetricallyWound with respect to ground potential 7 whereby the two halves of saidloop are in substantial electrostatic balance; a radio frequencyreceiver and amplifier connectedacross' one of said halves of the loop;a detector connected to said amplifier; anaudiofrequency amplifierconnected to said detector; a rectifier. connected to said audiofrequency amplifier for translating the output signals from said audiofrequency amplifier into'dlrect current nnpul'ses and a milhammeterconnected in said rectifier circuit and responsive to; sa d impulse,

2. In a radio direction finder system, a loop for receiving signals;means for grounding the midpoint of said loop, said loop beingsymmetrically wound with respect to ground potential whereby the twohalves of said loop are in substantial electrostatic balance; a radiofrequency receiver and amplifier forming the sole receiver electricallyassociated with said loop, said receiver being connected across only oneof said halves of the loop; a detector connected to said amplifier; anaudio frequency amplifier connected to said detector; a rectifierconnected to said audio frequencyamplifier for translating the outputsignals in said audio frequency amplifieri nto direct current signalsand a milliammeterconnected in said rectifier circuit and responsive tosaid direct current signals.

' 3L In a radio direction finder system, a loop for receiving signals;means for grounding the midpoint of said loop, said loop beingsymmetrically wound with respect to. ground potential whereby the twohalves of said loop are in substantial electrostatic balance; a receiverand amplifier forming the sole receiver electrically associated withsaid loop and having input circuit whose grid terminal is connected toone terminal of said loop and whose-cathode terminal is connected to thegrounded side of said loop; an output circuit for said receiverandarnpl-i fier; and a milliammete-r electrically connected in saidoutput circuit and responsive to said signals.

Signed at New York, in the county of New York and State of New York,this-24th day of April, 1929; A. D.

' J @SEPH' D. R. FREEIZL,

